1. Field of the Invention
The present invention relates to fireplaces, and, more particularly, to fireplaces inducing a flow of cooling air above the primary combustion chamber.
2. Description of the Related Art
A fireplace may be designed to be built into a wall during the construction of a new building. Because the fireplace is necessarily in proximity to certain combustible building products, e.g., wood, the temperature at a location a specified distance from the exterior of the fireplace should not exceed a predetermined relative temperature with respect to an ambient temperature, in accordance with certain standards in the industry. For example, in accordance with Underwriters Laboratory Standard U.L. 127, Standard for Factory Built Fireplaces (6th Ed., 1988), which is incorporated herein by reference, the predetermined relative temperature (e.g., 90.degree. F. or 140.degree. F. above an ambient temperature) is measured at a specified distance from the exterior of the fireplace (e.g., 1/2 inch) at the surface of a combustible building product.
It is known in the art to circulate air via a natural draft in an air flow duct disposed across the bottom, back and top of a fireplace and exhaust the cooling air into the combustion chamber. The cooling air reduces the exterior surface temperature of the fireplace, enhances secondary combustion within the combustion chamber and is exhausted up the chimney flue to the environment- A problem with such a design, however, is that radiant heat rising from the combustion chamber collides with the flow of cooling air and obstructs the flow of cooling air into the combustion chamber. Because the flow of cooling air is impeded from entry into the combustion chamber, the flow of cooling air across the bottom, back and top of the fireplace is likewise impeded. Decreased flow of cooling air across the bottom, back, and top of the fireplace results in decreased heat transfer via convection in the air flow conduit directly adjacent the combustion chamber and results in a higher exterior surface temperature of the fireplace- Therefore, what is needed in the art is a fireplace which causes an adequate flow of cooling air through the fireplace exterior of the primary combustion chamber.
As a result of the decreased cooling air flow and heat transfer, insulation is typically provided at strategic locations directly adjacent the exterior of the fireplace to maintain the temperature at a location a specified distance from the exterior of the fireplace below a predetermined temperature relative to an ambient temperature. Insulation disposed above the combustion chamber increases the height of the fireplace. Accordingly, what is needed in the art is a fireplace which does not utilize insulation above the primary combustion chamber and maintains the temperature at a location a specified distance from the exterior of the fireplace below a predetermined temperature relative to an ambient temperature. A further need is a fireplace which reduces the height of the fireplace above the combustion chamber.
It is also known in the art to induce a flow of cooling air in a conduit disposed above the primary combustion chamber for cooling the exterior of the fireplace. Such a fireplace is disclosed in U.S. Pat. No. 5,016,613, issued to the present inventor, which is assigned to the assignee of the present invention and incorporated herein by reference. In general, a primary wall and secondary wall disposed above the combustion chamber define a converging nozzle therebetween which induces a flow of cooling air which is exhausted into the chimney flue. Disposed above the secondary wall, between the secondary wall and upper exterior of the fireplace, is a dead air space. Insulation is attached to the exterior of the fireplace above the secondary wall to maintain the temperature at a location a specified distance from the exterior of the fireplace below a predetermined relative temperature with respect to an ambient temperature. The air flow conduit defined by the primary wall and secondary wall acts to decrease the exterior surface temperature of the fireplace.
Over a period of time, however, the temperature of the stagnant air between the secondary wall and exterior of the fireplace increases. Insulation attached to the exterior of the fireplace above the secondary wall is needed to maintain the temperature at a location a specified distance from the exterior of the fireplace below a predetermined temperature relative to an ambient temperature. U.S. Pat. No. 5,016,613 therefore is a step forward in the art toward reducing the exterior surface temperature of a fireplace, but still requires insulation to maintain the aforementioned relative temperature below a predetermined limit.
It may also be possible to reduce the exterior surface temperature of a fireplace without the use of insulation. For example, in applications where the size of the fireplace is not a prohibiting factor, a conduit may be formed around the bottom, back and top of the fireplace for circulating a flow of air, i.e., such as in a room air circulating fireplace. Such fireplaces use a forced flow of air to heat the room in which the fireplace is located. What is needed in the art is a fireplace having an adequate flow of cooling air through the fireplace exterior of the primary combustion chamber without additional hardware, such as a blower, for causing the flow of cooling air.